I. Field of the Invention
This invention relates to a duct that is provided for containing long runs of optical fibers, electric wires or the likes disposed in underground networks. More particularly, the invention relates to a multiple channel duct assembly which includes a plurality of contiguous ducts adapted for the containment of lengthy runs of for optical fibers, electric wires or the likes.
II. Description of the Prior Art
In the ground network industry, the proper design and installation of fiber optic cables or electric wires is critical to maintaining the integrity of the information or the electric energy carried by such cables.
Due to the delicate nature of the optic fibers or electric wires themselves, there is a need to protect the fibers or the electric wires from external sources of stress, such as temperature, pressure and contact with contaminating substances. As a result, most of the innovation in this industry has been directed to devising certain combinations of coverings to surround the optical fibers or electric wires. Therefore, a brief discussion of a method of installing fiber optic cable follows.
A multiple channel duct disclosed in U.S. Pat. No. 4,741,593, comprises a plurality of corrugated inner ducts contiguous, co-directionally extending, substantially parallel, in abutting contact with each other, each of said inner duct having a series of encircling contiguous convolutions extending over the length, being made up of contiguous ridges and troughs; and a flexible, synthetic resin overwrap sheath consisting of a sheath of rigid polyvinylchloride having a thickness of about 5 mils to about 15 mils, said sheath of rigid polyvinylchloride encircling and jacketing the corrugated inner ducts over their entire length to retain them in their contiguous relationship.
The above mentioned reference says that this type of multiple channel duct is flexible and can be coiled around relatively large reels. A great length of said multiple channel duct be coiled on the reel for lay out into an underground communications pipe, or can be reeled into a trench for direct burial. This type of multiple channel duct allows an overall reduction in fiber optic cable installation costs, and the manifolding aspect of the system maintains high structural integrity over the entire length of the conduit sections, and affords enhanced moisture protection to the entire system by reason of the overwrap employed. These advantages are the most desirable attributes in the cable duct for optical fibers, electric wires or the likes.
However, I have not found this type of multiple channel duct is sold in real cable duct market until now. The reason, I believe, is why this type of multiple channel duct has critical deficiencies in strength or flexibility in reality, which have not been found by the inventor at first. It is well known fact that although the inner duct of plastic with relatively small diameter, even though non-corrugated, is so flexible that it can be coiled around transportable reels, the non-corrugated outer duct of plastic with relatively large diameter is not so flexible that it can not be coiled around transportable reels.
The above-mentioned multiple channel duct include a plurality of corrugated inner ducts of plastic and a non-corrugated outer duct of plastic. Therefore, it is easily understood that the above-mentioned multiple channel duct is not so flexible that it can not be coiled around transportable reels. I believe that this deficiency is one of the reasons why this type of multiple channel duct can not be founded in real cable market.
A current method of installing fiber optic cables is disclosed in U.S. Pat. No. 5,027,864. That reference involves the use of a hollow outer duct, typically constructed of polyvinylchloride (PVC) in forty foot lengths, which provides the first level of protection from the elements underground. This outer duct acts as a conduit for the passage of a number of smaller tubes, or xe2x80x9cinner ductsxe2x80x9d typically constructed of polyethylene in continuously long run lengths, which provides the second level of protection from the elements underground. Each of these inner ducts has a number of external longitudinally extending ribs, and each inner duct may contain a single fiber optic cable or a plurality of such cables.
The method of installing the cables first requires the introduction of the inner ducts through the outer duct by pulling the inner ducts from a spool located on the surface. From an underground work area, a gripper is attached to one end of each inner duct, after which the inner ducts are drawn through the outer duct until they reside completely within the outer duct. Once the inner ducts are in place, the fiber optic cables are then drawn through each of the inner ducts by a pull string blown through each of the inner ducts. The resulting assembly, therefore, comprises a single fiber optic cable or a plurality of fiber optic cables within each of several inner ducts, with the inner ducts being surrounded by the protective outer duct. The ribbed design of the inner ducts is to purports to facilitate the installation and removal of cables for maintenance and repair.
While the above-described method of installation and housing of fiber optic cables does provide a certain level of convenience for maintenance and construction workers, as well as protection for the cables themselves, several deficiencies are apparent.
First, the material used for fabrication of the outer ducts, i.e. PVC, does not afford the flexibility for use with spools in lengths greater than forty feet. Thus, the labor costs in connecting segments of outer duct every forty feet adds a tremendous cost element to the overall project budget. Second, each outer duct connection site adds a point of structural weakness to the series of segments, as well as a site of possible contaminant infiltration from underground sources.
Further, the insertion of the inner ducts through the outer duct imposes a substantial increase in installation costs, in terms of labor. The other type of multiple channel duct is disclosed in U.S. Pat. No. 5,692,545. That reference involves a cable duct for protecting communication cable comprising an elongated body portion having a first end and a second end, the body portion further including a longitudinal axis extending between the first end and the second end; and at least two passageways formed completely through the body portion and extending substantially parallel to the longitudinal axis, each of the passageways having a cross sectional area sufficient to loosely contain at least one communication cable; wherein said body portion is constructed from a combination of materials including plastic and crumb rubber.
This type of multiple channel duct eliminates the inner ducts altogether, allowing extrusion of a duct to much greater lengths, and installation of such ducts from spools. Therefore this type of duct also has advantages in minimizing the number of connections required between segments of the duct and other protective attributes of the duct and increase the data transmission integrity of the cables themselves.
However, this type of duct has deficiencies inherent in construction from a combination of materials including plastic and crumb rubber. As described in the specification of said reference, if greater rigidity in said duct is required, a greater percentage of plastic may be added. Conversely, if greater flexibility is desired, a greater percentage of crumb rubber would likely provide the necessary flexion.
Therefore, it is difficult to meet the strict needs of greater strength and greater flexibility at the same time in this type of multiple channel duct. Besides, it is easily foreseen that this type of multiple channel duct with greater percentage of crumb rubber will have passageways with less smoothness on their inside surfaces. These might be critical deficiencies in the field of cable ducts, through which fiber optic cables, electric wires or the like are inserted.
It is an object of this invention to provide a multiple channel duct assembly which enables quicker installation of fiber optic cables, electric wires or the likes thus reducing labor and material costs substantially over the prior art.
It is another object of this invention to provide a multiple channel duct assembly which reduces the number of connections required between the duct segments themselves and has greater strength as well as greater flexibility at the same time.
It is still another object of this invention to provide a multiple channel duct assembly which has inner ducts with sufficiently smooth inside surfaces.
The multiple channel duct assembly for cables in accordance with the present invention comprises (a) a plurality of plastic inner ducts contiguous, co-directionally extending, substantially parallel, in abutting contact with each other, each of said inner ducts having the cross sectional areas sufficient to contain at least one cable; and (b) a plastic outer duct encircling said inner ducts over their entire length to retain them in their contiguous relationship; (c) wherein said outer duct has a corrugated tubular section including a plurality of contiguous ridges and troughs extending over the entire length; (d) whereby said assembly is so flexible that it can be coiled around transportable reels as well as so strong that it can withstand dirt in a trench.
The multiple channel duct assembly can be extruded incessantly to much greater lengths, being coiled around transportable reels. A great length of said multiple channel duct assembly be coiled on the reel for lay out into an underground communications pipe, or can be reeled 15 into a trench for direct burial.
This duct assembly allows an overall reduction in cable installation costs, and the manifolding aspect of the present invention maintains high structural integrity over the entire length of the conduit sections, and affords enhanced moisture protection to the entire system by reason of the outer duct which is corrugated and incessantly extended. Besides, the aspect of inner ducts of plastic with less friction provides sufficiently smooth inside surfaces to the inner ducts, through which fiber optic cables, electric wires or the likes are inserted.